Metal Arc Spraying / Thermal Spraying
Metal Arc Spray, (a process classified under Thermal Spraying) is an industrial coating process that utilises an electric arc to melt various coating wires, powders or ceramic rods. The molten material is then atomised by a high velocity air stream (typically compressed air) to create and propel a spray stream with specific required characteristics onto the surface being treated.
Thermal sprayed coatings are typically applied to metal substrates. Thermal sprayed coatings uniquely enhance and improve the performance of the component. Typical thicknesses of 0,4 – 6mm can be achieved.
Some examples of coatings applied with arc spraying:
- Pure metals (Cu, Al, Zn, Ni, Mo, Sn)
- Alloys (NiAl, CuSn, NiCr, NICu, …….)
The vast variety of material combinations allow arc spray to be used in a wide spectrum of industrial applications providing:
- Wear resistance
- Oxidation, shock and abrasion resistance
- Dimensional restoration
- Corrosion protection
- Electrical conductivity
High Velocity Oxygen Fuel Spraying
High velocity oxygen fuel spraying (HVOF), (a specialised Thermal Spraying process) is achieved when a mixture of gaseous or liquid fuel and oxygen is fed into a combustion chamber, where they are ignited and combusted continuously. The resultant hot gas at a pressure close to 1 MPa emanates through a converging–diverging nozzle and travels through a straight section. The fuels can be gases (hydrogen, methane, propane, polypropylene, acetylene, natural gas, etc.) or liquids (kerosene, etc.). The jet velocity at the exit of the barrel (>1000 m/s) exceeds the speed of sound.
A powder feed stock is injected into the gas stream, which accelerates the powder up to 800 m/s. The stream of hot gas and powder is directed towards the surface to be coated. The powder partially melts in the stream, and deposits upon the substrate. The resulting coating has low porosity and high bond strength.
HVOF coatings can be as thick as 12 mm. It is typically used to deposit wear and corrosion resistant coatings on materials, such as ceramic and metallic layers.
Some coatings applied via HVOF process include:
- Ni-/Co-based alloys/Stainless (Stellite, Triballoy, Inconel, …)
- Carbides / Cermets (WC-Co, Cr2C3-NiCr, …)
Typical applications of the HVOF process:
- (High) Wear resistance
- Sliding, abrasive, erosion, …
- Corrosion resistance (dense)
- Gasses, acids, salt water, …
- HT oxidation / corrosion
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